The present invention relates to a laminate comprising a saponified ethylene-vinyl acetate copolymer (hereinafter also referred to as EVOH) as an intermediate layer. More particularly, the present invention relates to a laminate superior in bag making property in that it affords a packaging bag having excellent gas barrier property, moisture proof, aromatic proof and the like, as well as superior sealing performance and appearance, particularly under high humidity.
In general terms, EVOH is superior in transparency, gas barrier property, aromatic proof, solvent resistance, oil resistance and the like, and in view of such superior properties, used for various packaging materials such as food packaging material, pharmaceutical preparation packaging material, industrial chemical packaging material, pesticide packaging material and the like. Moreover, EVOH is expected to replace conventional polyvinylidene chloride coating films (as used herein, a film includes a sheet).
To be specific, the EVOH is a laminate wherein an EVOH layer is laminated via an adhesive layer on the surface of a polyolefin film such as polypropylene (hereinafter to be also referred to as PP) and the like. The film is typically subjected to stretching in an attempt to improve mechanical strength and the like of the laminate.
When such laminate is used as various packaging films, however, the laminate is curled or twisted in response to heat, moisture and the like, due to differences of constituting resins in residual stress and relaxation shrinkage. When the laminate is formed into a packaging bag, the sealed portion thereof suffers from deformation and abnormalities, which may eventually affect the appearance and property of the packaging bag.
To cope with this problem, JP-A-58-33427 teaches absorption of not less than 0.5 wt % of water by a hygroscopic resin layer of the laminated film comprising a polyolefin resin layer and the hygroscopic resin layer (EVOH and the like).
However, according to the above-mentioned method, an EVOH layer (which is a barrier layer) absorbs water, such that the barrier property of the EVOH layer is degraded, failing to sufficiently utilize the barrier property of the EVOH layer, and the productivity of the laminated film is degraded due to the addition of a water absorption step.
U.S. Pat. No. 4,472,485 discloses an oriented film comprised of PP/adhesive resin/EVOH/adhesive resin.
Due to the propensity of EVOH toward lower gas barrier property because of moisture and humidity, however, when the corresponding oriented film is used as various packaging films, the gas barrier property under high humidity may ran out. Further, there is room for improving moisture proof as a packaging bag.
Thus, there is a strong demand for a laminate superior in bag making property and capable of affording a packaging bag excellent in gas barrier property, moisture proof, aromatic proof and the like, as well as sealing performance and appearance, particularly under high humidity.
It has been now found according to the present invention, that, a laminate obtained by co-extruding EVOH and an adhesive resin on one surface of a polypropylene (PP) film oriented at least uniaxially to give a laminate having a layer structure of PP/adhesive resin/EVOH/adhesive resin, stretching the laminate in the transverse direction (TD) and laminating a heat sealing layer on the surface of the adhesive resin of the laminate, can achieve the above-mentioned goal, particularly when the PP layer has a three-layer structure of polypropylene/hydrocarbon resin-containing polypropylene/polypropylene, and further, when the EVOH layer shows an orientation factor of the Cxe2x80x94O group of xe2x88x920.4 -0.01 as obtained by a polarized infrared dichroism method, and that the action and effect of the present invention can be fully exhibited.
Accordingly, the present invention provides the following.
(1) A laminate having a layer structure of A/C/B/C/D, which is obtained by the steps of
(a) coextruding a saponified ethylene-vinyl acetate copolymer (B) and an adhesive resin (C) on one side of a polypropylene film (A) oriented at least uniaxially, to give a laminate having a layer structure of A/C/B/C,
(b) stretching this laminate in the transverse direction, and
(c) laminating a heat sealing layer (D) on a surface of the adhesive resin (C) of the laminate.
(2) The laminate of (1) above, wherein the A layer has a three-layer structure of A1/A2/A1 wherein A1 is a polypropylene and A2 is a hydrocarbon resin-containing polypropylene.
(3) The laminate of (1) above, wherein the B layer has an orientation factor of a Cxe2x80x94O group as determined by a polarized infrared dichroism method of xe2x88x920.4-xe2x88x920.01.
(4) The laminate of (2) above, wherein the B layer has an orientation factor of a Cxe2x80x94O group as determined by a polarized infrared dichroism method of xe2x88x920.4-xe2x88x920.01.
(5) The laminate of (1) above, wherein the B layer comprises at least two kinds of saponified ethylene-vinyl acetate copolymers, a difference between a maximum ethylene content and a minimum ethylene content of the copolymers being not less than 4 mol %, or a difference between a maximum degree of saponification and a minimum degree of saponification of the copolymers being not less than 1 mol %, or a difference between a maximum ethylene content and a minimum ethylene content of the copolymers being not less than 4 mol % and a difference between a maximum degree of saponification and a minimum degree of saponification of the copolymers being not less than 1 mol %.
(6) The laminate of (2) above, wherein the B layer comprises at least two kinds of saponified ethylene-vinyl acetate copolymers, a difference between a maximum ethylene content and a minimum ethylene content of the copolymers being not less than 4 mol %, or a difference between a maximum degree of saponification and a minimum degree of saponification of the copolymers being not less than 1 mol %, or a difference between a maximum ethylene content and a minimum ethylene content of the copolymers being not less than 4 mol % and a difference between a maximum degree of saponification and a minimum degree of saponification of the copolymers being not less than 1 mol %.
(7) The laminate of (3) above, wherein the B layer comprises at least two kinds of saponified ethylene-vinyl acetate copolymers, a difference between a maximum ethylene content and a minimum ethylene content of the copolymers being not less than 4 mol %, or a difference between a maximum degree of saponification and a minimum degree of saponification of the copolymers being not less than 1 mol %, or a difference between a maximum ethylene content and a minimum ethylene content of the copolymers being not less than 4 mol % and a difference between a maximum degree of saponification and a minimum degree of saponification of the copolymers being not less than 1 mol %.
(8) The laminate of (4) above, wherein the B layer comprises at least two kinds of saponified ethylene-vinyl acetate copolymers, a difference between a maximum ethylene content and a minimum ethylene content of the copolymers being not less than 4 mol %, or a difference between a maximum degree of saponification and a minimum degree of saponification of the copolymers being not less than 1 mol %, or a difference between a maximum ethylene content and a minimum ethylene content of the copolymers being not less than 4 mol % and a difference between a maximum degree of saponification and a minimum degree of saponification of the copolymers being not less than 1 mol %.
(9) The laminate of (1) above, further comprising a translucent layer on the A layer, wherein the laminate has a haze value of not less than 30%.
(10) The laminate of (2) above, further comprising a translucent layer on the A layer, wherein the laminate has a haze value of not less than 30%.
(11) The laminate of (3) above, further comprising a translucent layer on the A layer, wherein the laminate has a haze value of not less than 30%.
(12) The laminate of (4) above, further comprising a translucent layer on the A layer, wherein the laminate has a haze value of not less than 30%.
(13) A method for producing a laminate having a layer structure of A/C/B/C/D, comprising the steps of
(a) coextruding a saponified ethylene-vinyl acetate copolymer (B) and an adhesive resin (C) on one side of a polypropylene film (A) oriented at least uniaxially, to give a laminate having a layer structure of A/C/B/C,
(b) stretching this laminate in the transverse direction, and
(c) laminating a heat sealing layer (D) on a surface of the adhesive resin (C) of the laminate.
(14) The production method of (13) above, wherein the polypropylene film (A) has a three-layer structure of A1/A2/A1 wherein A1 is a polypropylene and A2 is a hydrocarbon resin-containing polypropylene.
(15) A packaging bag comprising the laminate of (1) above.
(16) A packaging bag comprising the laminate of (2) above.
(17) A packaging bag comprising the laminate of (9) above.
(18) A packaging bag comprising the laminate of (10) above.